The aim of this research is to describe speech events at the acoustical, perceptual, and physiological levels, and to develop models of the speech production and perception processes. Current work includes examination of the acoustic and articulatory properties of certain speech sounds, and the formulation of rational bases for the classification of these sounds in terms of distinctive features. Of particular interest are the spectral and temporal characteristics of stop, nasal and fricative consonants. The characteristics of timing and fundamental-frequency variations in sentences are studied, as well as the recording of speech sounds that occurs when these sounds are placed in words in sentences. Studies of the ability of observers to decode spectrograms of sentences into phonetic units have shown that 80 to 90 percent of the phonetic units can be identified from the visual display of the acoustic data. Procedures for automatic simulation of the processes of phonetic recognition and lexical access are being developed.